<style>
    h1{
        color: red;
        font-size: 18px
    }
    #hi{
        color: black;
    }
    .hello{
        color: green;
    }
</style>

<body>
   <h1>你好呀👏</h1> 
   <h1 class="hello">你好呀👏</h1> 
   <h1 class="hello">你好呀👏</h1> 
   <h1 id=hi>你好呀👏</h1> 
</body>